Does THE GAME count on this list?

I lost... :'(

Rick Astley can win it easily

Not sure if this counts, but would "Legand of Zelda: Sord of Atari" (sic) be a valid example of game that is hard to 100%? I made the game myself and I can't even beat the 1st dungeon (it's actually possible, though)

Also Ghosts n' Goblins (at least on the NES) and Super Ghouls n' Ghosts (to a lesser extent) are other examples.

SNES games I own I find hard to 100%:
Donkey kong country: Level memorization and fast reflexes are required to make it trough the levels. In world 3 I cannot get past stage 3-1. I did it once, but I couldn't save...
Last action hero: Stage 1 is unbeatable especially if you try really hard. I don't even want to play this game.
Super metroid: Not because it's a hard game, but some secrets remain well hidden.
Super mario world: Because of that castle with the moving platform snake on which you have to stand for the entire stage.
Super R-type: I finally got to stage 3 only to get my ass handed to me.
Street fighter II: On normal mode ofc. Some of the non-playable fighters just kick my ass with cheaty special moves.

For the PSX: Alundra. It's a zelda-style game.

A little bit of both.

Super Crate Box (not mine, the original by Vlambeer). While I did more than 200 in normal mode, I can't get past 40 in SFMT and 14 in Ambush ;_;